In recent years, there has developed many uses for hollow microspheres of uniform diameter, uniform wall thickness and uniform strength. Hollow microspheres have found industrial uses as filler materials and as proppants to increase gas recovery from gas wells. Though there are known methods for producing hollow microspheres the known methods do not suggest addition of fibers to substantially improve the tensile strength of the hollow porous microspheres.
The above mentioned copending Torobin U.S. Ser. No. 639,126, filed Aug. 9, 1984, discloses a method and apparatus for producing hollow porous microspheres, but does not disclose the addition of reinforcing fibers to the microspheres to improve the tensile strength of the microspheres.
The known methods for producing hollow porous microspheres include Sowman U.S. Pat. No. 4,349,456 (sol gel process), hollow multicel microspheres De Vos et al. U.S. Pat. No. 4,059,423 (latent blowing gas process), and hollow microspheres Beck, U.S. Pat. No. 4,111,713 (mechanical agglomeration). Beck incidently mentions the addition of glass fibers to the materials forming the hollow microspheres. Methods of forming hollow fused microspheres are disclosed in Torobin U.S. Pat. No. 4,303,431 (glass), Torobin U.S. Pat. No. 4,303,603 (plastic), and Torobin U.S. Pat. No. 4,415,512 (metal).
Prior to the time applicant made the present invention there was no known simple economical method of producing fiber reinforced hollow microspheres or fiber reinforced hollow porous microspheres where the microspheres were substantially spherical, of substantially uniform diameter and uniform wall thickness and where the microspheres had reinforcing fibers uniformly distributed in the walls of the microspheres.